奀豬mami,
My situation is also same as you. I got pregnant when my first baby is 13 months old. Thou I still keep breastfeeding her until she is 16 months I decide to stop. Because I dont want her to feel upset when I start to feed the 2nd baby with breast milk. And I think to stop earlier will help her to forget how much she like breastmilk. I didnt change her to formula either. My 2nd baby is now 3wks old. And my 1st child didnt felt left out at all.